Supporting means for vacuum electrodes



Jan. 8, 1952 c. F. ROBINSON SUPPORTING MEANS FOR VACUUM ELECTRODES FiledOct. 31, 1949 JNVENTOR. 0/4245: xFfloa/Msml,

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Patented Jan. 8, 1952 SUPPORTING MEANS FOR VACUUM ELECTRODES Charles F.Robinson, Pasadena, Calif., assignor to Consolidated EngineeringCorporation, Pasadena, Calif., a corporation of California ApplicationOctober 31, 1949, Serial No. 124,641

This invention relates to vacuum tubes and more particularly, toimprovements in electrode mounting within such tubes.

The invention provides a complete and simple solution to the troublesomeproblem of supporting electrodes in precise geometrical relation withina vacuum system. The difiiculty arises from the fact that suchelectrodes must be insulated from each other and yet preferably mountedto each other to insure a fixed spatial relationship. Thus, to achievegeometrical precision, it is desirable that the electrodes be tiedtogether in some fashion, it being virtually impossible to maintain afixed spatial relationship between independently mounted electrodes.Moreover, in many instances, as for example, mass spectrometry, it isdesirable to tie the electrodes together as a unit for the additionalreason that such construction simplifies removal of the electrodes fromthe vacuum system. A mass spectrometer having such a unitary electrodeassembly and incorporating the structure of the present invention isdescribed in detail with respect to the drawing.

The use of insulating ties or spacers suggests itself as one possiblesolution. However, any insulation serving as a structural member in avacuum system in the presence of electrical fields must satisfy thefollowing requirements:

1. The insulation must not liberate gas into the system either byinherent vapor pressure or by porosity at temperatures ranging betweenabout 100 C. and 500 C.

2. The insulation must be dimensionally stable at temperatures in theabove range.

3. The insulation must not carbonize or track when subjected to ion orelectron bombardment or electrical flashovers.

4. The insulation should be inexpensive. That is. it should be capableof being fabricated to close tolerances or should be availablecommercially at close tolerances and at low cost.

13 Claims. (01. 313-81) The first three of the above requirementseliminate plastics and virtually every other insulating material exceptglass, synthetic sapphires, fused quartz, or similar vitreousrefractories. However these materials in the forms of tubing, rods,sheets, or other special shapes do not satisfy the dimensionallimitations of the fourth requirements since commercially availableforms are generally molded to very loose tolerances, and if held toclose tolerances, are very expensive.

Very recently, vitreous refractories, such as Pyrex glass and syntheticsapphire mono-crystals have, become commercially available in sphericalform to very close tolerances in the order of magnitude of plus or minus.00005 of an inch.

I have now developed an electrode mounting arrangement wherein thesespherical refractories are used to space and also to locate a pluralityof electrodes within a unitary structure. The invention provides, in avacuum tube having a plurality of electrodes, means for holding theelectrodes in fixed geometrical relationship comprising a plurality ofinsulating spacers separating the electrodes and clamping means:clamping the electrodes against the spacers. Various modifications aremade in the above arrangement for particular applications. For example,it is frequently necessary, as in the case of mass spectrometry, toshield any insulating surfaces from an ion beam, etc., with a conductiveshield. Various means for accomplishing such shielding are illustratedin the accompanying drawing in which: i

Fig. 1 is a sectional elevation showing a plurality of electrodesmounted together in accordance with the invention; and

Fig. 2 is a sectional elevation through an ion source of a massspectrometer with the electrodes of the ion source being held in fixedgeometrical relationship in accordance with the invention.

Fig. 1 shows the general principles of the mounting means of theinvention and comprises a plurality of electrodes ill, I I, l 2, held toa single tie plate M by means of a plurality of tie bolts l6, extendingthrough the tie plate and screwed into the outermost electrode l0. Priorto assembling the electrode structure, the several electrodes and tieplate are drilled in a jig to form the holes 10A, IDB in electrode II),the holes HA, H3 in electrode ll, holes IZA, [2B in electrode l2 andholes MA, MB in tie plate [4. Although shown in the drawing as beingaligned, the holes in the several electrodes need not be thus arrangedprovided only that adjoining electrodes are provided with aligned holes.However, alignment through all the electrodes constitutes preferredpractice since it reduces the drilling to a.minimum and also tends toinsure more accurate results since only a single jig need be employed.

A glass ball of the type described and of somewhat larger diameter thanthe holes in the electrodes is placed between adjacent electrodes toseat in the aligned holes therein. Thus, a glass ball 98 is interposedbetween electrodes l0 and l I seating in the aligned holes IDA, HA. Asecond glass ball [9 is interposed between the same electrodes seatingin the other aligned holes IIJB, MB in these two electrodes. To insurestability, three or more such spacers are provided between each pair ofelectrodes and seating in similar aligned holes. A third spacer ball 20is partially apparentbetween the electrodes Ill and II. In a similarfashion, electrodes l I and I2 are spaced from each other and areaccurately held in fixed geometrical relationship by a plurality ofglass balls, and the electrode 12 is similarly arranged with respect totie plate 16. There need be no direct connection between tie plate [6and the intermediate electrodes II and I2, a single series of tie boltsclamping the outermost electrode H] to the tie plate will hold all ofthe electrodes together since the spacer balls [8, I9, 20, etc., holdthe electrodes in fixed position, there being no possibility of lateralshift.

The accuracy with which the electrode positions are predetermined isafunction of the ac.-

' pattern is an important advantage of the invention. It is frequentlydesirable andsometimes necessary, to dismantle such an electrodestructure for cleaning and repairs. With an arrangement as shown in Fig.1, such procedure is a simple matter involvingonly the removal of thetie-bolts I6, I7 and separation of the electrodes. When the unit isreassembled the electrodes will inherently bear the same geometricalrelationship to each'other with .a possible error of only .0001 of aninch. There is no other electrode-structure in use today which can bedismantled and re assembledwith such case and such accuracy. Evengreater accuracy may be achieved by peening the corners of the .drilledholes to the radius of the spacing balls in asimple hydraulic oriimpactpress using commercially available highly accurate .carbolly or. othersuitable ball for the peening hammers. r

The spacing between the electrodescan becpreselected .within very broadlimits. Pyrex balls ranging in size from to A, of an inch are availablecommercially, permitting electrodes spacing of from about A,; of an inchto approximatelyv Man inch or greater without adopting specialtechniques. If desired, closer spacing can be; obtained with oversizedballs, as for ex,- amplal/ of an inch separation may be obtained withinch balls by countersinking one of the seating holes.

Although the arrangement show in Fig. 1 illustrates the electrodes ashaving the seating holes extending all the way through the electrode,and the several seating holes in the separate electrodes are all alignedfrom top to bottom ofthe stack, neither of these features is alimitation on the invention. It is apparent that all that is required isa very shallow hole in which the'spacing balls may seat and it is notnecessary that the spacing balls between the electrodes l0 and H seat incontinuationsv of thesameholes in which the spacing balls betweentheelectrodes H and I2 are located. However, from a manufacturingstandpoint, it isconvenient to stack the electrodes. and tie plate in ajig and drill through the stack to form the arrangement shown in Fig. 1.

The invention. is particularlyapplicable to use in the ion source of amass spectrometer. As is well known, a mass spectrometer is ananalytical instrument for sortingand measuring ions according to theirmass-to-charge ratio. Such a trodes.

mass spectrometer includes an ion source in which the molecules of a gassample are ionized by bombardment with an electron beam or by otherknown methods and are propelled from'the ionizing region and into ananalyzer tube by means of pusher and accelerating electrodes. The usualarrangement includes a pair of coplanar pusher electrodes through whichgas molecules are introduced into the path of an electron beam, a firstaccelerating electrode having a slit therein through which the ions, asthey are formed, are propelled under the influence of a potentialbetween the pusher and first accelerating electrode and a second andthird accelerating electrodes through which the ions pass, beingaccelerated in their travel between'the several electrodes. To establishdifferent potentials onthe several electrodes, it is, of course,necessary that they be insulated from each other. Recent developments inmass spectrometry have resulted in an ion source, in which all of theelectrodes are mounted from a single insulated mounting plate by,separate tie rods, the tie rods connected to any given electrode passingthrough oversized holes in the intermediate electrodes.

'An ion source generally similar to that described above is illustratedand described inv considerable detail in co-pending United States patentapplication, Serial No. 33,596, filed by Clifford E. Berry on June 17,1948, now Patent No. 2,548,859, granted April17, 1951. The ion sourceshownin this co-pending application is reproduced with certainmodifications in sectional elevation in Fig. 2. Referring to thisfigure, the ion source comprises an insulating plate 22 a firstconductive plate 23, a, second conductive plate 24 overlying the firstplate and in engagement there- ,with and beinghollowed out to form anionization chamber 26, and accelerating electrodes 28 and 29. A sampleinlet tube 32 extends through the insulating plate and first conductive.pl'ate, opening into the ionization chamber 26. A pair of'pusherelectrodes 34, 34A are mounted in the ionization chamber 26 andare separated by a passageway 34B through which gas molecules pass fromtheinlet tube 32 into the region of the; ionization chamber above thepusher elec- A transverse electron beam originating from a source 36 ispassed through ionization chamber to ionize the molecules therein. ,Apotential difference is established between the pusher electrodes 34,34A, the conductive plate 24 and the successive accelerating electrodes28, 29,. The function of this ion source is toionize sample molecules inthe ionization chamber and to propel, them from the chamber throughslits 21, 21A, 2B in the succeeding accelerating electrodes so that'theyissue through the electrode 29 at a high velocity. Detailed descriptionof the functioning of an ion source and of amass spectrometer wouldaddnothing to an understanding of the invention.

Asmentioned above, it is necessary in an electrode structure wherein anion beam is produced,

to shield any insulating surfaces from-the beam so that surface chargeswill not develop 'on such surfaces. -The development of surface'chargeson insulating surfaces, the adverse effect of such surface charges onmass spectrometer operation contact with each other, may be weldedtogether. However, the accelerating electrodes 28 and 29 mustnecessarily be separated from the plate 24 and from each other. In Fig.2 I have shown two methods of spacing these electrodes in accordancewith the invention wherein the insulated balls are shielded or locatedso they cannot see the ion beam. Either of the two means shown in thedrawing may be used to .the exclusion of the other, the single drawingserving merely to show the alternative means.

The electrode 28 is provided with an annular axially projecting shoulder28A which extends into an annular groove 24A formed in the adjacentplate 24. The electrode 28 is drilled through the shoulder at 38, 39 andas many other locations as desired and the plate 24 is drilled to formthe holes 40, 4| opening into the groove 24A. The holes 38, 39 in theelectrode 28 are aligned with the holes 40, 4|, respectively, in theplate 24 and glass balls 44, 45 are seated in the two pairsof alignedholes in the same manner as shown in Fig. 1. It will be seen that thereis no direct path between an ion beam passing through the slit 21, 21A,21B and the glass balls 44, 45.

To hold the electrodes 28, 29 in fixed spatial relation, holes 48, 49are drilled in the electrode 29, and holes 50, 5| are drilled in theelectrode 29 in alignment with holes 48, 49. The holes 50, ii arecountersunk at their upper end and tubular members 54, 55 are affixedtherein projecting upwardly toward the electrode 29. The inside diameterof the tubular members 54, 55 is equal, within very close tolerances, tothe inside diameter of the holes 44, 49 in electrode 29. A convenientway of forming this arrangement is to tap the upper surface of theelectrode 28 and weld or press-fit a length of bar stock therein, havingthe outside diameter of the tubular members 54, 55. The electrodes 28,29 may then be placed in a jig and the holes 59, 5!, 48, 49 drilledtherein and through the bar stock. The net result will be as shown inFig. 2. The holes 48, 49 in electrode 29 are likewise countersunk attheir lower end and sleeves 58, 59 are afiixed therein as by swaging,welding or otherwise, the sleeves 58, 59 being of larger diameter thanthe corresponding tubes 54, 55 and projecting downwardly to encircle theupper ends of these tubes. Spacing balls 60, 6! are seated between theholes 48, 49 and the corresponding tubes 54, 55, respectively, toinsulate the two electrodes from each other and to fix their spacialrelationship. Although the drawing of Fig. 2 illustrates only twospacing balls between each of the two electrodes, it is apparent thatthree or more spacers represent preferred construction since two ballswill not prevent tipping of the electrode.

A plurality of tie rods 64, 65 are connected between the insulated plate22 and the uppermost electrode 29, passing through oversized passagewaysin the intermediate conductive plates and electrodes. The tie rods 54,65 are conveniently fused through the insulated plate 22 in the mannerdescribed in the aforementioned co-pending application and the electrode29 is held thereon by nuts 66, 51, respectively. In this manner, theelectrode 29 exerts a compressive force on the intervening electrodeswhich hold the spacing balls snugly, preventing any shift of theelectrodes with respect to each other.

One major differentiating feature between the ion source illustrated inFig. 2 and the ion source illustrated in said co-pending application isthe matter of tying the electrodes to the insulating plate. In anattempt to achieve fixed geometrical relationship between theelectrodes, it has been the practice heretofore to weld each of theelectrodes to tie rods extending from the insulating plate. One bigdrawback of this type of construction is the dlfficulty of tearing downthe structure for cleaning, etc., and re-assembly. Because of the use ofthe insulated spacers in accordance with the invention as shown in Fig.2, there is no need to weld the tie rods 64, to the electrode 29 and infact, there is no need of providing tie rods from the insulating plateto the intermediate electrodes since they are all clamped in position bythe single group of tie rods and are held in this position by thespacing balls.

In Fig. 2, the pusher electrodes are shown diagrammatically only. Theymay be spaced from the plate 23 by means of spacing balls as shown inthe same manner as in the diagram of Fig. l or in the manner of theplates 28, 29. The simpler arrangement may be used since the spacers arenot exposed to any ion beam, being effectively shielded by th pusherelectrodes themselves. Separate tie rods must of necessity be usedbetween the pusher electrodes and the insulating plate since thecompressive force exerted between the insulating plate and the outermostelectrode 29 has no effect on the pusher electrodes. In apparatuswherein separate tie rods are required for each successive electrodes,these tie rods are used also as electrical leads. In the apparatus shownin Fig. 2, the tie rods connecting the insulating plate and electrode 29may be used as electrical leads in the same manner. Since, however, notie rods are required between the plate and the intermediate electrodes,any type of rigid or non-rigid leads may be carried through the plateand connected with the appropriate electrodes.

The invention is not limited in accordance with the drawing anddescription thereof. Although the holes in adjoining electrodes areshown to be of equal diameter and to extend through the electrodes, theyneed not be formed in this manner. All that is necessary is that theadjoining holes in which a single spherical spacer is seated be coaxialand be deep enough to receive the spacer. If the holes are of differentsize the spacer will merely seat deeper in the face of one electrodethan in the face of the adjoinin electrode. There will be no sacrificeof accuracy so long as the two holes are coaxial. Also, the mountingmeans shown in Fig. 2 whereby the spacers are shielded from the ion beamare not adapted exclusively to use in the ion source of a massspectrometer. Other vacuum tubes in which insulating surfaces requireshielding, as for example, electron guns, high frequency triodes, etc..are preferably constructed using one or the other, or both, of theshielding means shown in Fig. 2.

I claim:

1. In a vacuum tube having a plurality of electrodes, means for holdingthe electrodes in fixed geometric relationship comprising a plurality ofspherical insulating spacers disposed between adjacent electrodes andseating in spaced, axially aligned cavities formed in said adjacentelectrodes, and clamping means clamping the electrodes against thespacers.

2. In a vacuum tube having a plurality of superposed electrodes, meansfor holding the electrodes in fixed geometric relationship comprising aninsulating mounting plate, a plurality of spherical insulating spacersdisposed between adjacent electrodes and seating in aligned 7 cavitiesformed in adjoinin faces of adjacent electrodes, and clamping means forclamping the electrodes between an outer electrode and the mountingplate, the clamping means being insulated 'from the intermediateelectrodes,

3. In a vacuum tube, an electrode assembly comprising a plurality ofelectrodes having a-plurality of holes therein, the holes in oneelectrode being aligned with and the same diameter as the holes in anadjoining electrode, a plurality of spherical insulators disposedbetween the electrodes and seating in the aligned holes, and meansclamping the electrodes together against said insulators so that theelectrodes are spaced from each other by said insulators and heldagainst lateral shift by-theinsulators seating in said'holes.

'4. In a mass spectrometer ion source having a plurality of electrodeswith aligned slits therein for passage of an ion beamtherethrough,'means for holding said electrodes in fixed geometricrelationship comprising a plurality of sphericalins'ulators seating inaligned cavities in adjoining faces of adjacent electrodes, meanspreventing the spacers from seeing the ion beam and means clamping theelectrodes against the spacers.

5. In a mass spectrometer ion source having a plurality of electrodeswith aligned slits therein for passage of an ion beam therethrough,means for holding saidelectrodes in fixed geometric relationshipcomprising an insulating mounting plate, a plurality of sphericalinsulators disposed between adjacent electrodes and seating in cavitiesformed in adjoining faces of said adjacent 2.

through holes in the intermediate electrodes of larger diameter than thebolts.

7. In a mass spectrometer ion source having at least two plate typeelectrodes with aligned slits therein for passage of an ion beamtherethrough,

means for spacing said electrodes-in fixed-geometric relationshipcomprising an annular groove in the adjoining face of one of saidelectrodes, an annular lip in the adjoinin face of the-other electrodeextending into said 'groove without touching said one of saidelectrodes, a plurality of spherical insulators disposed in said grooveand seating in aligned cavities formed in the bottom of said groove andouter face of said lip; and means clamping the electrodes againstsaid-insulators.

8. Apparatus according to claim 7 wherein said cavities are formed by aplurality of aligned holes in each electrode opening into said grooveand the outer face of said lip respectively.

9. In a mass spectrometerion sources having at least two plate typeelectrodes with aligned slits therein for passage ofan ion beamtherethrough, means for spacing said-electrodes in fixed geometricrelationship comprising a series of aligned pairs of holes in theelectrodes, the several holes being countersunk in adjoining faces ofthe electrodes, a tubular member afllxed in the countersunk portion ofeach hole and projecting towardthe other electrode one of said tubularmembers of each aligned pairheing of larger diameter than the othertubular member of each pair and extending concentrically over the end ofsaid other tubular. member without touching it, aplurality of sphericalinsulators disposed between said electrodes between the end of saidother of said tubular members of each pair and the aligned hole in theadjacent electrode, and means for clamping the. electrodes against saidinsulators. '10. Apparatus according toiclaim 9 wherein the hole in thesmaller tubular memberin each pair is the same diameter as the hole inthe electrode carrying the companion tubularmember ofthe pair. 1

ii. In a vacuum tube having at leasttwo electrodes, means for spacingsaid electrodesin-fixed geometric relationship comprising an annulargroove in the adjoining face of one of said electrodes, an annular lipin the adjoining face of the other electrode extending into said groovewithout touching said one of said electrodes, a plurality of sphericalinsulators disposed in said groove and seating in aligned cavitiesformed in the bottom of said groove-and outer face of-said lip, andmeans clamping the electrodes against saidinsulators. 1

12. In a, vacuum tube having at least twoelectrodes, means for spacingsaid electrodes in fixed,

countersunk portion of each hole and projecting toward the otherelectrode one of said tubular members of each aligned pair being oflarger diameter than the other tubular member of each pair and-extendingconcentrically over the end of said other tubular member without,touching it, a plurality of'spherical insulators disposed between theend of said other of said tubular members of each pair and the'alignedhole'in-the adjacent electrode, and means for clamping the electrodesagainst said insulators. 13. Ina vacuum tube having a plurality ofsuperposed electrodes, means for holding the electrodes in fixedgeometric relationship comprising aninsulating mounting plate, aplurality of spherical insulating spacers disposed between adjacentelectrodes andseatedi'n aligned cavities formed in adjacent faces ofadjacent electrodes, mounting posts extending from the mounting platethrough aligned holes in-the zseveral elecltrodes independent of thespacers, the aligned holes in the electrodes being larger than the,posts to provide an annular insulating'gap, and-clamping means affixedon the ends of the posts :and insulated from the proximate electrode toclamp the electrodes-against the spacers.

CHARLES F. ROBINSON.

REFERENCES CITED The following references are of record in'the is ofthis patent: V

V UNITED STATES PATENTS v Numher

